1. Field of the Invention
This invention relates to a probe for an optical sensor used to measure the degree of oxygen saturation in hemoglobin and the hemoglobin concentration in blood or an organism. More particularly, the present invention relates to an optical sensor probe used by being inserted in an extracorporeal circulation circuit such as a pump-oxygenator circuit to continuously monitor the degree of oxygen saturation in hemoglobin and the hemoglobin concentration.
2. Description of the Related Art
For open heart surgery or the like, extracorporeal circulation is temporarily effected by using a pump-oxygenator instead of the heart and the lung of the organism. To know the oxygen transport rate of blood circulation and the oxygen consumption in the organism during the extracorporeal circulation, the degree of oxygen saturation in blood in arteries and veins and the hemoglobin concentration thereof are measured by periodically sampling the blood. In this system, the oxygen saturation cannot be continuously examined. There is therefore a risk of a delay of the desired treatment for an abrupt change in the physical state of the subject or patient. A method for preventing such a risk is well known in which the blood of the subject is irradiated with light having a particular wavelength and the degree of oxygen saturation is obtained from the intensity of the reflected light or transmission light. Measurement of hemoglobin concentration has also been studied but no method for measuring this factor with accuracy has been established.
Conventional detectors for detecting the intensity of light reflected in blood are designed to be immersed in blood to detect the intensity of reflected light and therefore entail the following problems. During immersion in blood for a long time, characteristics of circuit component parts are changed under the influence of the temperature of the blood and so on, and the value of the intensity of reflected light detected is thereby changed, resulting in difficulty in measuring the hemoglobin concentration and other quantities with accuracy. There is also a risk of leakage of electricity since electric circuit parts are immersed in blood. PG,4
Moreover, in the case of monitoring based on continuous measurement of the hemoglobin concentration, the intensity of reflected light cannot be measured with stability and accuracy due to the influence of the size and shape of blood cells although the intensity of reflected light is correlative to the hemoglobin concentration.